Method and machine for treating textile materials by ammonia or other liquids

ABSTRACT

The machine comprises: a path for the textile article (T); along the path impregnation means ( 11, 13 ) to impregnate the textile article with said product; means ( 23, 25 ) to remove the product from said textile article. The impregnation means may comprise one or more cooled rollers ( 11, 13 ) on which the product condenses and around which the textile article to be treated is driven.

TECHNICAL FIELD

The present invention relates to a method for treating textile materials by ammonia, in particular bolts of fabric or yarns. This type of method is commonly known as mercerization. More generally, the invention relates to a method for treating textile articles or materials by liquids at low condensation temperature.

The invention also relates to a machine for treating textile materials.

STATE OF THE ART

Mercerization is a typical treatment for fabrics and yarns made of all cellulosic fibers, particular for cotton, which allows the material to be given a series of advantages, such as:

-   -   increase in luster and hydrophilicity,     -   increased dimensional stability,     -   increased yield of the dye,     -   an improvement and intensification of subsequent finishing         treatments (i.e. anti-crease treatments).

Currently, the mercerization process is performed with the use of alkalies, generally caustic soda, which determines:

-   -   shrinkage and swelling of the fiber,     -   increased tensile strength,     -   decreased flexural and torsional strength.

The section of the fiber is transformed from elliptical to circular, thus allowing improved reflection of light with a consequent increase in luster. Alternatively, liquid ammonia can be used as the mercerization chemical.

The treatment of cotton fabrics by liquid ammonia is a finishing process that influences the technological textile properties of the fabric by structural changes deeply rooted in the fiber. This process has noteworthy potential for development; it is suffice to think that the contact times required to implement mercerization through immersion in liquid ammonia are extremely short (often below one second). During this type of treatment the fabric is impregnated with liquid ammonia in percentages of generally no less than 100% in weight and dried rapidly to limit the consequent extremely rapid shrinking process before this becomes unacceptable.

From the state of the art of research performed by various research institutes it is known that treatment by liquid ammonia makes it possible to obtain special mercerization effects that cannot be obtained with traditional mercerization methods using caustic soda, not to mention better quality results in the dyeing and finishing processes (crease resistance, increase in fiber strength, swelling of the fiber and luster), obtaining an increase in comfort and in the functional and aesthetic performances of the finished product.

An example of mercerization machine with ammonia is described in U.S. Pat. No. 3,980,429. In these machines the fabric is fed continuously and travels through a chamber provided with an impregnation bath, in which the fabric is immersed to become impregnated with ammonia. Drying means, typically in the form of heated rollers, which cause evaporation of the ammonia from the fabric, are disposed downstream of the impregnation bath. Before the fabric passes over the heated rollers it can be pressed to eliminate a part of the ammonia with which it is impregnated. A complex system is then provided for recovery and subsequent liquefaction of the gaseous ammonia to return the liquefied ammonia to the bath.

There are very few machines in the world that use this technology, due to the difficulties linked to the use of liquid ammonia, which at atmospheric pressure evaporates at −33° C. This makes the machines complicated to construct and causes problems related to safety and to disposal of processing waste. As a result, the machine is very complex and costly.

Discontinuous mercerization machines were recently proposed. In these machines a bolt of fabric wound on a roller is disposed in a closed chamber, where it is gradually unwound, immersed in an impregnation bath containing liquid ammonia, dried and rewound on a pick-up roller. An example of a discontinuous machine of this type is described by C. Meyer <<Nuovo proce-dimento di trattamento discontinue con ammoniaca>> (“New procedure of discontinuous treatment by ammonia”), in ITB, International Textile Bulletin June 1999, page 48 and following.

In discontinuous machines it is also necessary to recover and liquefy the gaseous ammonia.

The high level of toxicity of ammonia makes procedures for its recovery and liquefaction particularly complicated and critical.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to produce a method and a machine that overcomes the drawbacks described above. More specifically, according to a first aspect, the object of the present invention is to produce a method that makes the mercerization process with ammonia simpler and less expensive, as well as intrinsically safer, and more generally a method wherein a textile article is impregnated with products that at ambient pressure condense at low temperature.

According to a different aspect, the object of the present invention is to produce a machine that is simpler and easier to manage, as well as less expensive and safer, for mercerization with ammonia or for other treatments implying impregnation of textile materials with products that at ambient pressure condense at low temperature.

The method according to the invention is defined in claim 1 and the machine according to the invention is defined in claim 20. The dependent claims define characteristics and non-limiting preferred embodiments of the invention. Textile material or article is intended as any semi-finished product of considerable length that maybe fed along a treatment path. In particular, the textile article or material may be a spun fabric, a knitted fabric, a non-woven fabric or an essentially tubular product produced with spun or unspun textile fibers. The textile article or material may, moreover, also be a yarn with any structure.

In substance, the method according to the invention performs controlled impregnation of the fabric with liquid ammonia that is made to condense from the gaseous or vapor state directly on the fabric or on a surface with which the fabric comes into contact, in a quantity sufficient to implement the process.

With this system the quantity of ammonia that impregnates the fabric can be reduced in a controlled way to any percentage value required. On the contrary, all systems currently in use perform impregnation by immersion, or other equivalent systems, which transfer to the fabric percentages in weight of ammonia much greater than 100%, if not followed by pressing, or only slightly less than 100% if followed by pressing, with the consequent need to remove extremely high quantities of this substance from the fabric.

It must be borne in mind that the fabrics involved in the treatment, which are cotton, linen and hemp in particular, are extremely quick to absorb the ammonia and distribute it in all their fibers, but are much more reluctant to release it. Repeated experiments and analyses have shown that the percentages of ammonia required for the treatment are considerably lower than the values currently employed in traditional machines, said values simply being the inevitable outcome of the fact that in traditional machines and methods the fabric is immersed and soaked completely with ammonia.

In practice, the method according to the invention to obtain condensation of the gaseous ammonia on the fabric consists in rapidly cooling the fabric, immersed in an environment saturated with gaseous ammonia, placing it in contact with surfaces maintained suitably cold with a cooling system capable of controlling the temperature. The time for which the fabric remains in contact with the cold surface and the temperature thereof allow safe and repeatable control of the percentage of impregnation of the fabric. The pressure of the ammonia gas chosen to saturate the treatment chamber, which due to incompatibility with the environment must be isolated from the outside environment, will also determine the temperature range to which the fabric must be taken to obtain condensation of the ammonia. Tests performed on various samples of linen and cotton showed that the same results are obtained both by immersing the fabric in liquid ammonia, with a degree of impregnation between 100% and 300% according to the traditional technique, and with the condensation process according to the present invention regulated in order to release variable percentages, for example between 5% and 10%, of ammonia in the fabric.

In the above and in the description below specific reference is made to the treatment of textile material using ammonia. In fact, in this application the method and the machine according to the invention have specific and important advantages, as indicated above and as shall be explained in greater detail below. However, the same method may also be used to treat textile articles by other products which at the treatment pressure are made to condense from a saturated atmosphere, to be absorbed rapidly and in small quantities by the textile article.

In principle, the cooled surface can be a fixed surface, on which the textile article is made to run. Preferably, however, one or more guide rollers, motorized or idle, are provided, on which the textile article is guided and which are maintained at the temperature required to obtain condensation of the ammonia present in the saturated atmosphere of the chamber in which said rollers are disposed.

One of the possible configurations, although not the only one, is to feed the fabric maintaining it in contact with the two cooling rollers, on one of which the fabric is partially wound with the right side and on the other with the wrong side.

The rollers or other members defining the condensation surface of the ammonia, are enclosed in a treatment or impregnation chamber, filled completely with gaseous ammonia at a pressure in the vicinity, for example, to the ambient pressure, so that the rollers or any other condensation surface must be maintained at temperatures below −33° C. by means of a suitable cooling circuit. In these conditions condensation of the ammonia will take place both on the fabric and on the cooled metallic surface immediately before the fabric comes into contact and absorbs it immediately. Subsequently, in an adjacent drying chamber, the fabric will advance in contact with heated rollers, or other drying devices and the ammonia vapor released from the fabric will return to the treatment or impregnation chamber to be condensed once again on the fabric fed to the chamber. Advantageously, the two condensation and drying chambers are in fluid communication, so that condensation of the ammonia in the first causes gaseous ammonia to be retrieved from the other. In theory, if all the ammonia is removed from the fabric before the latter leaves the drying chamber, the machine does not require the addition of any ammonia or complex systems to recover and liquefy said ammonia.

All in all, the impregnation process by condensation according to the invention differs from other traditional methods in two particularly important aspects:

-   -   1) the quantity of ammonia utilized during the process is         considerably lower, even by 10 to 20 times compared to         traditional methods, with a consequent reduction in the         dimensions and costs of the drying and ammonia recovery systems;     -   2) it is unnecessary to add liquid ammonia to the process, with         the consequent elimination of the costly system to compress and         liquefy the ammonia recovered from the fabric drying system.

In principle, the process may be a continuous process, with the textile article fed through an open system, that is with an inlet and an outlet. Alternatively, however, the process and machine may be produced for discontinuous treatment, in which a bolt of fabric or reel of yarn or another textile article is unwound and rewound in a closed environment, from which the treated textile article is collected at the end of the treatment after said treatment is interrupted.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall be better understood by following the description and accompanying drawing, which shows non-limiting practical embodiments of the invention. More specifically, in the drawing:

FIG. 1 shows a schematic longitudinal section of an exemplificative diagram of a machine according to the invention in an embodiment for continuous treatment; and

FIG. 2 shows a schematic section of a machine for discontinuous treatment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the diagram in FIG. 1 the machine, indicated as a whole with 1, is of the continuous type and has an inlet 3 and an outlet 5 for the textile article, which in this example of embodiment is a fabric indicated with T. However, the treatment may also be performed on a yarn or on another type of textile article the fibers of which must undergo mercerization using ammonia. Means, of a per se known type (not shown), may be associated with the inlet 3 and the outlet 5, to prevent the gases present inside the machine from escaping.

Schematically the machine is provided with a first condensation or impregnation chamber, that is for the actual treatment, indicated with 7, communicating with a second drying chamber 9. The path of the fabric T to be treated extends and travels through the two chambers.

Two rollers 11, 13 are disposed in the impregnation chamber 7 and rotate in opposite directions according to the arrows in the drawing. The rollers may be motorized to facilitate feed of the fabric, or one of them may be idle and the other motorized. Alternatively they may both be idle. The solution with idle rollers simplifies the roller support system, but the fabric must to be made to travel through the impregnation chamber 7 by traction. For this purpose one or more of the rollers downstream along the path of the fabric may be motorized. The number 15 schematically indicates a cooling circuit used to compress, cool, condense and expand the coolant made to circulate in the two rollers 11 ad 13. The chamber 7 is saturated with ammonia at a controlled pressure, for example slightly below the atmospheric pressure, to prevent ammonia from escaping from the chamber into the environment. By maintaining the rollers 11, 13 at a temperature below −33° C. the ammonia condensates or T the surface of the rollers and impregnates the fabric T which is driven around them. As both faces of the fabric come into contact with the rollers, this allows essentially uniform impregnation of the thickness of the fabric.

The fabric exits from the impregnation or treatment chamber 7 through a passage 17 and enters the drying chamber 9, where a dancer roll 18 determines the correct tension of the fabric and automatically adjusts the speed of the subsequent controlled rollers. In the chamber 9, as well as being wound around the dancer roll 18, the fabric is also wound around guide and drive rollers 19, 21, 27 that define a path of the fabric around two heated rollers 23, 25. These may be heated electrically, by the circulation of hot air, by a heat-carrying liquid or vapor or in any other suitable way. In the same way as the condensation rollers 11, 13, the drying rollers 23, 25 are disposed so that they come into contact with the two opposed faces of the fabric T to cause rapid and uniform drying.

The ammonia that evaporates from the fabric T by means of absorption of heat energy supplied by the rollers 23, 25 is returned to the chamber 7 through the passage 17. In this way no machine of any type is required to recover the ammonia. Recovery and re-use of the ammonia occurs as a result of the difference in the thermodynamic conditions in the two chambers.

The condensation conditions in the chamber 7 and the feed speed of the fabric T can be controlled to obtain impregnation of the fabric with low percentages in weight of ammonia, typically and advantageously below 50% in weight of the dry fabric and preferably equal to or below 25%. In particular, the textile article may be impregnated with a quantity ranging from 1% to 20% in weight, and in particular from 1% to 15% in weight, and even more preferably from 1% to 10% or from 1% to 8% in weight. This small percentage of ammonia may be eliminated very easily and more or less completely by the heated rollers 23, 25.

As is known to those skilled in the art, ammonia dissolved in water does not perform any useful effect on the fabric. Considering that the fabric subjected to the treatment necessarily has a humidity content relevant to a greater or lesser extent (typically ranging from 2% to 8% but in any case depending on the ambient humidity and on any pre-treatments of the textile article), it must be borne in mind that part of the ammonia absorbed by the fabric is neutralized by the water present in the fabric in the form of humidity. Water absorbs up to 40% in weight of ammonia. Therefore, if the fabric has a humidity percentage of, for example, 5% in weight compared to the weight of the dry fabric, a quantity equal to 2% in weight of the dry fabric will be absorbed by the water and neutralized by it. To obtain a useful quantity of ammonia, for example equal to 3% in weight of the dry fabric, impregnation must be carried out with a total quantity of 5% in weight of ammonia, with reference to the weight of the dry fabric.

Therefore, the percentages indicated above must be intended as useful or available percentages of ammonia. Useful percentage is intended as the percentage of ammonia that remains available to perform its action on the textile fibers, after that the residual water in the form of humidity in the fabric has been saturated by the ammonia.

FIG. 2 shows an example of embodiment of a discontinuous machine.

The same numbers indicate parts that are the same as or correspond to those in the machine in FIG. 1.

The machine, once again indicated as a whole with 1, comprises a first impregnation and treatment chamber 7 and a second drying chamber 9. Two rollers 11, 13 cooled to a suitable temperature, typically to −33° C. or lower, are provided in the impregnation chamber 7. A feed path of the textile article, which also in this case is represented by way of example by a fabric T, extends around the two rollers 11, 13. The fabric is unwound from a feed roll R1 on which a certain quantity of fabric to be treated is wound. The roll R1 is unwound by a motorized unwinding roller 2. The number 4 indicates two counter-pressure rollers associated with two cooled rollers 11, 13.

In this embodiment a scraper 6 with a heating pipe 8 and a drainage tray 10 is also associated with each of the two cooled rollers 11, 13. This layout may be used to scrape away any water ice forming on the surface of the rollers. The ice is detached by the scraper, which may be positioned at a minimum distance from the surface of the roller so as not to scrape the ammonia condensate. The detached ice is heated by means of the heating pipe and recovered by means of the drainage tray.

The number 12 indicates spreader bars used to prevent wrinkles from forming on the fabric T, so that it adheres perfectly to the respective roller 11 or 13.

The fabric impregnated with ammonia through contact with the condensation rollers 11, 13, passes through a passage 17 to enter the drying chamber 9. Here two heated rollers 23, 25 are provided, around which the path of the fabric T, said path also defined by guide rollers 18, 19, extends. The roller 18 may be a dancer roll to control tension of the fabric T. Further spreader bars 12 are also provided along the path of the fabric and in the impregnation chamber 7. The treated and dried fabric is wound on a roll R2, made to rotate by a motorized winding roller 30.

The machine operates as follows. A roll R1 of fabric to be treated is fed into the chamber 7 and its initial end is made to pass through the path and fastened to a winding core on which the roll R2 will be formed. The machine is closed and the fabric is treated being unwound from the roll R1 and rewound on the roll R2. At the end of the treatment, after elimination of the ammonia from the machine or in any case with due caution, the roll R2 is removed from the chamber 9 and a new roll R1 is inserted in the chamber 7 to be subjected to a new treatment cycle.

In the example shown in FIG. 2, the fluid passes from the chamber 9 to the chamber 7 through a separate path with respect to the path of the fabric. In fact, a heat insulated wall 33 is provided to separate the two chambers and define, together with a cold wall 35, cooled by a cooling coil 37, a cavity 39. This communicates with the chamber 9 through a top opening 39A and with the chamber 7 through a bottom opening 39B. The evaporated ammonia in the chamber 9 enters the cavity 39 through the opening 39A and is delivered cooled to the chamber 7 through the bottom opening 39B. As well as the function of cooling the ammonia to facilitate condensation in the impregnation chamber 7, the cooling coil 37 also has the function of causing condensation of any water vapor released by the fabric during the drying phase. The condensed water is collected by a drainage tray 40 that closes the cavity 39 at the bottom. This allows elimination or reduction of the entry of water vapor in the impregnation chamber 7 housing the elements at low temperature on which the ammonia condenses. Water condensate may form on the cooled wall 35. This may be eliminated by means of heating when required. For this purpose a second coil, or other heating and defrosting means, for example using electrical resistance, may be provided.

The particular layout of the cavity 39 with the coil 37 and any other heating means for defrosting, and the other elements combined with it, may also be provided in the continuous machine in FIG. 1. The expedients for eliminating water vapor, water condensate or ice are particularly useful in the case of a continuous machine, where the continuous passage of the fabric may cause water to accumulate. Therefore, the presence of the elements 4, 6, 8, 10, 12 may also be provided and advantageous in the continuous machine in FIG. 1.

One or more guide rollers defining the path of the fabric in the impregnation chamber 7 may be adjustable to modify the path of the fabric and to increase or reduce the contact surface between the fabric and the cooled rollers 11, 13. This allows a greater or smaller percentage of the surface of the rollers to be made available for direct condensation of the ammonia. In this way it is possible to modify the quantity of ammonia that condenses on the surface of the rollers and impregnates the fabric when it comes into contact with the roller. In fact, impregnation can take place by condensation of the ammonia from the atmosphere of the chamber 9 on the exposed surface of the fabric cooled by the rollers, or by condensation on the surface of the rollers and absorption by the fabric upon contact. In this case, impregnation takes place through the surface of the fabric in contact with the roller rather than through the surface exposed to the atmosphere of the chamber 7.

It is understood that the drawing purely shows a possible embodiment of the invention, which may vary in forms and layouts without however departing from the scope of the concept on which the invention is based. For example, the ammonia, or any other treatment product, may also be eliminated using a different method to heating, such as through evaporation caused by vacuum pressure, by washing or in another way. On the other hand, heating is the least expensive method and allows immediate re-use of the evaporated product, by cooling and transferring it to the impregnation chamber. Moreover, the fabric may also be subjected to further operations upstream and downstream of the treatment described herein. In particular, if removal of the treatment product (ammonia or another) by evaporation is not sufficient, a subsequent wash phase may be provided. These operations may take place in line in the case of the continuous line in FIG. 1, or outside the line by unwinding the roll R2 in the case of the machine in FIG. 2. 

1. A method for treating a textile article by a product at low condensation temperature, comprising the phases of wetting the textile article with said product in liquid state and making the liquid product act on the fibers of the textile article; characterized in that the textile article is impregnated by condensation of said product from the gaseous state to the liquid state.
 2. Method as claimed in claim 1, characterized in that said product is ammonia.
 3. Method as claimed in claim 1, characterized in that the textile article is brought into contact with at least one cooled surface in an environment saturated with said product in gaseous state, the product condensing on said cooled surface and being absorbed by the textile article in contact with it.
 4. Method as claimed in claim 1, characterized in that said textile article is a continuous article.
 5. Method as claimed in claim 4, characterized in that said textile article is a bolt of fabric treated in width.
 6. Method as claimed claim 1, characterized in that said textile article is a yarn.
 7. Method as claimed in claim 1, characterized in that the textile article is impregnated with a useful quantity of said condensed product no greater than 50% and preferably no greater than 25% and even more preferably ranging from 1% to 20% in weight of the dry textile article.
 8. Method as claimed in claim 7, characterized in that the textile article is impregnated with a useful quantity of said product ranging from 1% to 15% in weight, and preferably from 1% to 10% or from 1% to 8% in weight of the dry textile article.
 9. Method as claimed in claim 1, characterized in that said product is condensed on at least one moving surface around which said textile article is driven.
 10. Method as claimed in claim 9, characterized in that said at least one moving surface is the cylindrical surface of a rotating guide roller.
 11. Method as claimed in claim 10, characterized in that said textile article is driven around two cooled guide rollers, one in contact with a first surface of the textile article and the other in contact with the opposed surface of the textile article.
 12. Method as claimed in claim 1, characterized in that the product is removed at least partially from the textile article after said product has acted on said textile article.
 13. Method as claimed in claim 12, characterized in that said product is removed from said textile article by means of evaporation.
 14. Method as claimed in claim 13, characterized in that the product evaporated from the textile article is condensed to once again impregnate a different portion of said textile article.
 15. Method as claimed in claim 13, characterized in that the impregnated textile article is heated to cause removal of the product by evaporation.
 16. Method as claimed in claim 15, characterized in that said textile article is heated by driving it around two heated rollers, in contact with the two opposed surfaces of the textile article.
 17. Method as claimed in claim 1, characterized in that: an impregnation chamber and a drying chamber, in fluid communication, are disposed along a feed path of the textile article; the textile article is impregnated with said condensed product in said impregnation chamber; the impregnated textile article is transferred from the impregnation chamber to the drying chamber; the product is removed by evaporation from the textile article in said drying chamber; the evaporated product in gaseous state is transferred from the evaporation chamber to the impregnation chamber.
 18. Method as claimed in claim 1, characterized in that said textile article is treated continuously.
 19. Method as claimed in claim 1, characterized in that said textile article is treated discontinuously.
 20. Machine for treating a textile article by means of a product in liquid phase at low condensation temperature, comprising: a path for the textile article; along said path impregnation means to impregnate the textile article with said product; means to remove the product from said textile article; characterized in that said impregnation means cause condensation of the product from the gaseous state to wet said textile article.
 21. Machine as claimed in claim 20, characterized in that said impregnation means comprise at least one cooled surface, the textile article coming into contact with said cooled surface on which said product condenses.
 22. Machine as claimed in claim 21, characterized in that said at least one cooled surface is the cylindrical surface of a guide roller of the textile article.
 23. Machine as claimed in claim 22, characterized in that a scraper is associated with said cooled roller to eliminate any water ice.
 24. Machine as claimed in claim 20, characterized in that it comprises two cooled rollers, to drive the textile article, said rollers being disposed along the path of the textile article so that a first of the surfaces of said textile article is in contact with the first of said rollers and the second of its surfaces is in contact with the second of said rollers.
 25. Machine as claimed claim 20, characterized in that it comprises an impregnation chamber, containing 07n atmosphere of said product in gaseous state, in which said impregnation means are disposed.
 26. Machine as claimed in claim 25, characterized in that it comprises a drying chamber, in which said means to remove the product from the textile article are disposed, the textile article traveling through said impregnation chamber and said drying chamber, disposed in series along the feed path of the textile article.
 27. Machine as claimed in claim 26, characterized in that said impregnation chamber and said drying chamber are in fluid communication, the product removed from the textile article in said drying chamber being transferred in gaseous state towards said impregnation chamber and being condensed therein.
 28. Machine as claimed in claim 27, characterized by a cavity between said drying chamber and said impregnation chamber, the evaporated product traveling through said cavity, in which cooling means are disposed.
 29. Machine as claimed in claim 28, characterized in that means to recover and remove water are associated with said cavity.
 30. Machine as claimed in claim 20 to 29, characterized in that said means to remove the product from the textile article comprise at least one heated roller.
 31. Machine as claimed in claim 20, characterized in that said path for the textile article is a continuous path with an inlet and an outlet.
 32. Machine as claimed in claim 20, characterized in that it comprises unwinding means to dispense the textile article from a first supply of textile article to be treated and winding means to recover the treated textile article and place it in a second supply of treated textile article, a path extending between said unwinding means and said winding means.
 33. Machine as claimed in claim 20, characterized in that said impregnation means may be taken to conditions of pressure and temperature that condense ammonia. 